Discussion of Related Art
Electromagnetic radiation of various frequencies is radiated from many devices used in a wide range of facilities including homes, workplaces such as offices, manufacturing and military installations, ships, aircraft and other structures. Examples of such devices include computers, computer monitors, computer keyboards, radio equipment, communication devices, etc. If this radiation escapes from the facility, it can be intercepted and analyzed for the purpose of deciphering data associated with or encoded in the escaped radiation. For example, technology exists for reconstructing the image appearing on a computer monitor in a building from a remote location outside the building or from a location within a building by detecting certain wavelength frequencies from the monitor screen even if the monitor screen is not in view from the remote location. This is accomplished by known techniques wherein certain frequencies of light from the monitor screen, even after being reflected from various surfaces inside the building or room where the monitor is located, escape and are intercepted and analyzed by an eavesdropper in another location outside the building or room where the monitor is located. Obviously, the ability of an eavesdropper to intercept such radiation constitutes a significant security risk that is desirably eliminated from facilities where secrecy is essential.
Although walls, such as brick, masonry block or stone walls may effectively prevent the escape of light frequencies from a facility, radio frequencies pass through walls that are not properly grounded to prevent such passage. Moreover, windows or other openings allow the passage of radiation to the outside where it can be intercepted, and permit entry of various forms of radiation, such as laser beams, infrared, and radio frequencies, into the facility. As a result, sensitive or secret data may be gathered from within the structure.
Indeed, the United States Government has long been concerned by the fact that electronic equipment, such as computers, printers, and electronic typewriters, give off electronic emanations. The TEMPEST (an acronym for Transient Electromagnetic Pulse Emanation Standard) program was created to introduce standards that would reduce the chances of leakage of emanations from devices used to process, transmit, or store sensitive information. This is typically done by either designing the electronic equipment to reduce or eliminate transient emanations, or by shielding the equipment (or sometimes a room or entire building) with copper or other conductive materials. Both alternatives can be extremely expensive.
The elimination of windows and other openings from a structure would obviously minimize the above-noted security risk. The disadvantages of a windowless or enclosed structure, however, are self-evident. It would be highly desirable, therefore, to prevent the escape of radiation associated with data through windows, doorways, or other openings while allowing other radiation to pass therethrough so that the enjoyment of the visual effects provided by such openings can be obtained without an undue security risk.
In addition to the security risks associated with the passage of certain wavelengths of electromagnetic radiation, acoustic transmission through a window, door or other opening also poses a security risk. It would be of additional benefit if transmission of both acoustic and the aforementioned electromagnetic radiation through openings could be minimized or avoided while preserving the visual benefits provided thereby.
The need for reducing the undesirable effects of the sun-its heat, excessive energy usage, glare, and ultraviolet (UV) radiation-has led to the development of solar control window films. Solar control window films are thin polyester sheets that are mounted on the glass windows of buildings and automobiles via an adhesive. It is said that such films are effective in providing comfort, visibility, and increased energy efficiency.
In the current workplace or home environment, however, there is a need for more protection than solar control films can provide. For example, it is important to protect the work product of an individual, business, or other entity from unauthorized data collection through the glass windows or other openings of their offices. The conventional solar control films described above are, for the most part, incapable of rejecting the wide range of frequencies used for such unauthorized data and information exchange.
Given the importance of security in today's competitive marketplace, a system that could preserve the privacy of the workplace is very desirable. Such a system would provide both comfort and security that in turn can bring about many benefits, including increased productivity and the preservation of confidentiality in both the public and private sectors.